Chapter 9 Notes

Question 1

Chemotrypsin uses covalent catalysis. How?

Answer 1

hydrolizes peptide bonds only after large hydrophobic residues

Question 2

Name an allosteric effector.

Answer 2

2,3-BPG

Question 3

Homotrophic/heterotrophic allosteric effector examples?

Answer 3

homotrophic: oxygen binding
heterotrophic: doesn’t look similar in terms of molecules they affect - doesn’t look like oxygen binding of 2,3-BPG

Question 4

How does covalent catalysis work?

Answer 4

Enzyme goes under acylation and forms acyl-enzyme. Water then comes in and breaks the O=C bond through deacylation to get a new enzyme

Question 5

Explain the catalytic triad.

Answer 5

Asp 102 stabilizes the positive charge and makes His 57 a better proton acceptor. His 57 then makes a powerful nucleophile, Ser 195; Asp uses the negative charge to stabilize the positive charge of His to make the powerful alkoxide ion

Question 6

In the peptide hydrolysis mechanism by chymotrypsin, why only large hydrophobic residues?

Answer 6

the answer is in the structure of chymotrypsin - has large pocket by active site where large aromatic groups can attach (brings peptide bond close to Ser)

Question 7

What groups attach in the S1 pocket of chymotrypsin?

Answer 7

cleaves large hydrophobic residues

Question 8

What groups can attach in the S1 pocket of trypsin?

Answer 8

can’t anchor hydrophobic groups because of the Aspartate residue in the S1 pocket and needs positively charged groups

Question 9

What groups would you see attach to the S1 pocket of an elastase residue?

Answer 9

very specific for only small AA chains (alanine, serine) due to the two Valines attached in the S1 pocket

Question 10

If Ser, His, and Asp are all changed to Ala, why would you see the same activity?

Answer 10

in uncatalyzed there are no groups; these groups are allowing the enzyme activity to increase (go faster); enzyme acts as a chemical catalyst (still has activity, but no groups); can still bind and mobilize substrates in correct orientation